Ok thanks, I have now messaged them.
I received my A3i today & it is very much faulty... It blows both T4A fuses at power on.
I have tested the rectifier diodes/1000uf caps/output transistors & all are fine
Would the LED/Q8 issue cause the fuses to blow ?
Right, just re-read the entire thread & it sounds like the LED's are at fault. I wonder what would happen if they were replaced with red ones ?
Green LED's drop about 2v, red LED's typically drop 1.7v. They are used as reference voltages to current sources made by Q8 and Q10. Using red LED's will probably lower the current through them a bit.
Fuses blowing is usually a sign of failed output transistors.
Fuses blowing is usually a sign of failed output transistors.
Thanks for that. I didnt want to risk it so have ordered some green ones... Puzzling as the outputs test perfect, guess I'll have to wait and see what happens after changing the leds/q8/q10.
cheers for the help.
Make up a bulb limiter cable (search diyaudio for details) so if you have any fault in the amp, the bulb will light and prevent parts from burning.
Well back again with more problems in 2 CA A3i ( and bring this thread back to life)
Got my hands in 2 more amps in a car boot sale for song but they don't sing 🙁
Got the first one open to find out that someone already made some of the changes our friend Alex suggested namely the driver transistors.
He made a mistake with diode D211 ( reversed ) and the problem is that 2 leds light up (L1 and L101) and the relay latches on.
I have put the diode in the right position and now the leds L2 and L102 light up but not the L1/101 and no relay activity.
Any ideas before I start to remove the transistors on that side of the supply ?
Ric
Got my hands in 2 more amps in a car boot sale for song but they don't sing 🙁
Got the first one open to find out that someone already made some of the changes our friend Alex suggested namely the driver transistors.
He made a mistake with diode D211 ( reversed ) and the problem is that 2 leds light up (L1 and L101) and the relay latches on.
I have put the diode in the right position and now the leds L2 and L102 light up but not the L1/101 and no relay activity.
Any ideas before I start to remove the transistors on that side of the supply ?
Ric
Got the first one working but...
Q8 and Q10 (108/110) get very hot and from what I read that is normal but I would like to know if is possible to get them cooler without having to put some type of heatsink
Anyone ?
Q8 and Q10 (108/110) get very hot and from what I read that is normal but I would like to know if is possible to get them cooler without having to put some type of heatsink
Anyone ?
No easy way. They really needed to be TO-126 devices. When you can get TO-92 heatsinks for 30p, theres not really much point.
Humm, ok
I think I have a few (old) new BD139/40 somewhere in my parts bin to replace the BC639/40.
I think I have a few (old) new BD139/40 somewhere in my parts bin to replace the BC639/40.
At one point BD139/140 was the same die as BC639/BC640. This is no longer true though. I think you may reduce performance of the circuit by doing this.
I would say KSA1381/KSC3503 but they are faster devices and may make the circuit unstable without modifications.
I would say KSA1381/KSC3503 but they are faster devices and may make the circuit unstable without modifications.
By old I mean very old, I have brand new BD135/6 and BD139/40 with around 15 years.
I can always put in the MJE243/253 that X-PRO recommended.
I'm preparing an parts order for Farnell and a couple more transistors is not going to brake the my bank account (50xIRFP240 and a few other bits).
Ric
I can always put in the MJE243/253 that X-PRO recommended.
I'm preparing an parts order for Farnell and a couple more transistors is not going to brake the my bank account (50xIRFP240 and a few other bits).
Ric
New problem
Replaced the BC639/640 with BD139/140 (original Philips one from the 90s) but they still get very hot and after a few tracks on the cd player it just shuts of (no sound )
I'm I missing something ?
Some small heatsinks on the BDs ?
The bias is set to 15mv
Replaced the BC639/640 with BD139/140 (original Philips one from the 90s) but they still get very hot and after a few tracks on the cd player it just shuts of (no sound )
I'm I missing something ?
Some small heatsinks on the BDs ?
The bias is set to 15mv
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Ok, got this one working with the BD139/140 replacing the BC639/640 with a bias of 10mV.
On the the second one (DOA) I found a missing zener diode (ZD1) and a faulty ZVP3306...
After replacing the missing/faulty parts the amp worked fine (+/-2 hours), set up the bias to 10mV closed the amp power it up and nothing.
After looking for obvious faults I found out that the ZVP3306 was dead again...
Any ideas what can be causing the Fet to fail ?
Ric
On the the second one (DOA) I found a missing zener diode (ZD1) and a faulty ZVP3306...
After replacing the missing/faulty parts the amp worked fine (+/-2 hours), set up the bias to 10mV closed the amp power it up and nothing.
After looking for obvious faults I found out that the ZVP3306 was dead again...
Any ideas what can be causing the Fet to fail ?
Ric
Hi everybody
Sorry for my english.
Very interesting thread.
I just look for serivice manual of A3i, my unit is faulty and i have only a partial schematic,
after some time it get very very hot.
I found my A3i in the trash, some jerk threw it away.
Gianni
Sorry for my english.
Very interesting thread.
I just look for serivice manual of A3i, my unit is faulty and i have only a partial schematic,
after some time it get very very hot.
I found my A3i in the trash, some jerk threw it away.
Gianni
In case you didn't see the OP schematic and comments or search the web yet:
cambridge audio a3i Service Manual free download,schematics,datasheets,eeprom bins,pcb,repair info for test equipment and electronics
cambridge audio a3i Service Manual free download,schematics,datasheets,eeprom bins,pcb,repair info for test equipment and electronics
Hello all,
Thanks a lot for all the useful informations on this forum and for the schematics.
I also got mine in a bin, in a dirty state (traces of burn inside, fuses blown, short circuit inside).
I replaced the 4 leds (burned) and several cap and resitor around them (mainly for security reasons).
I cleaned everything and also replaced one 2SA1216 in short circuit, setted the biases to 12mv then the A3I was back to life and givign me a very nice sound.
Since then, I still have a strange problem: the 2 F4A250V fuses are occasionally blowing, the 2 at the exact samle time. The amp can work for 3 months without loosing its fuses or for only a couple of hours.
The mesured DC voltage is higher than it should (+38,8V, -38,8V), when it should be +34V -34V according to schematics.
AC voltage mesured is 29V/29V, but I cannot find the value it should be.
-What is your ideas for the reason of this over range voltage ?
-What should I check/do to fix this ?
Thanks a lot in advance,
Nicolas (from france)
Thanks a lot for all the useful informations on this forum and for the schematics.
I also got mine in a bin, in a dirty state (traces of burn inside, fuses blown, short circuit inside).
I replaced the 4 leds (burned) and several cap and resitor around them (mainly for security reasons).
I cleaned everything and also replaced one 2SA1216 in short circuit, setted the biases to 12mv then the A3I was back to life and givign me a very nice sound.
Since then, I still have a strange problem: the 2 F4A250V fuses are occasionally blowing, the 2 at the exact samle time. The amp can work for 3 months without loosing its fuses or for only a couple of hours.
The mesured DC voltage is higher than it should (+38,8V, -38,8V), when it should be +34V -34V according to schematics.
AC voltage mesured is 29V/29V, but I cannot find the value it should be.
-What is your ideas for the reason of this over range voltage ?
-What should I check/do to fix this ?
Thanks a lot in advance,
Nicolas (from france)
I appreciate that this thread is six years old but I was interested in connecting with anyone who can advise on this amp.
I have had one for some years and today it has decided to retire.
The fault it has developed is that after a few minutes it cuts off and no sound is delivered to the speakers although the cd or cassette player is still functioning and can be heard via headphones direct from device.
I have never had an amp that has developed a fault and so am at a little bit of a loss. If such is an obvious problem for you experts I would be grateful to learn how to repair if such is possible.
If repair is not possible then I need to find an amp that likes classical music and would like to pair with Rogers speakers LS4a 150w 8ohm.
John
I have had one for some years and today it has decided to retire.
The fault it has developed is that after a few minutes it cuts off and no sound is delivered to the speakers although the cd or cassette player is still functioning and can be heard via headphones direct from device.
I have never had an amp that has developed a fault and so am at a little bit of a loss. If such is an obvious problem for you experts I would be grateful to learn how to repair if such is possible.
If repair is not possible then I need to find an amp that likes classical music and would like to pair with Rogers speakers LS4a 150w 8ohm.
John